Criminals typically use bots to infect large numbers of computers. These computers form a network, or a botnet.
Criminals use botnets to send out spam e-mail messages, spread viruses, attack computers and servers. If your computer becomes a part of a botnet, your computer might slow down.
For ways to help protect your computer from becoming a zombie in a botnet, go tohttp://www.microsoft.com/protect/computer/viruses/zombies.mspx